Three-way exhaust gas catalytic converters (hereinafter referred to as catalytic converters for simplicity) have proved their worth for a long time now as a means of reducing exhaust emissions in an internal combustion engine. In an internal combustion engine at normal operating temperature, up to 98% of the hydrocarbon, carbon monoxide and nitrogen oxide emissions can be converted by means of commercially available systems.
The emission behavior is unsatisfactory during cold starting and the immediately following warming-up phase of spark-ignited internal combustion engines, since at these times the catalytic converter and the lambda probe have not yet reached their operating temperatures.
A possible measure for improving the exhaust gas quality consists in introducing fresh air (referred to as secondary air) into the exhaust manifold close to the exhaust valves so that the exhaust gas constituents that were not combusted during starting due to a rich mixture are oxidized by afterburning at temperatures of up to 600° C. This exothermic reaction leads to an increase in the exhaust gas temperature and hence to a shortening of the warm-up or light-up time of the catalytic converter. The unburnt exhaust gas constituents are reduced at the same time.
A so-called secondary air pump is employed to introduce the secondary air. Said secondary air pump is an electrically driven compressor which draws in air from the environment and injects it into the exhaust gas tract close to the exhaust valves via secondary air lines into which a shutoff valve, which as a general rule is of the pneumatic type, is inserted.
The secondary air charger constitutes a powerful alternative to the electrically driven secondary air pump. Said secondary air charger consists of a turbine and a compressor, the turbine being driven by the pressure difference at the throttle valve in the intake tract. The compressor is disposed in a secondary air bypass to the throttle valve and delivers fresh air into the exhaust gas tract.
In internal combustion engines having a plurality of cylinders, e.g. 6, 8, or 12 cylinders, the cylinders are assigned to what are termed cylinder banks. In an 8-cylinder internal combustion engine, for example, the cylinders 1-4 are assigned to a first cylinder bank and the cylinders 5-8 to a second cylinder bank. In this arrangement each cylinder bank can be supplied with air by means of its own secondary air pump having associated secondary air lines or a single secondary air pump supplies both cylinder banks, in which case a line connected to the pump outlet then branches off and a secondary air line leads to each of the individual cylinder banks. This results in a bank-selective secondary air injection.
Since the secondary air system constitutes an exhaust-gas-relevant component within the motorized vehicle driven by means of the internal combustion engine, it must be checked for any faults that may occur. Future legislative measures (ARB, Air Resources Board, LEV II) provide that not only must the secondary air system as such, i.e. globally, be checked with regard to proper operation, but that in a system comprising a plurality of cylinder banks and consequently a plurality of secondary air paths, each individual subsystem must also be diagnosed and a bank-selective differentiation made in the event of a fault.
DE 41 20 891 A1 describes an internal combustion engine having a secondary air pump in which the delivery performance of the secondary air pump is monitored. Toward that end, the actual performance is compared with the desired performance at defined operating points.
DE 43 43 639 A1 discloses a method for monitoring a secondary air system wherein a first value is calculated which characterizes the secondary air stream blown into the exhaust gas channel of the internal combustion engine by the secondary air system. The first value is calculated from the air stream supplied to the internal combustion engine, from the air/fuel ratio of the mixture drawn in by the internal combustion engine and from the air/fuel ratio prevailing in the exhaust gas channel downstream of the secondary air line. The first value is compared with a predefined interval and in the event of a deviation a malfunction of the secondary air system is detected.
DE 197 13 180 C1 discloses a method for monitoring the secondary air mass flow of an exhaust gas purification system for an internal combustion engine. Secondary air is fed by means of a secondary air pump to an exhaust gas duct of the internal combustion engine upstream of an exhaust gas catalyzer, the measured signal of a secondary air mass meter being recorded. The variation in time of the measured signal is determined and a malfunction of the secondary air supply is detected if the variation does not correspond to a predetermined variation.
EP 0 928 366 B1 discloses a secondary air system for an internal combustion engine which has a secondary air pipe which is connected to an intake tract via an inlet orifice and to an exhaust gas tract via an outlet orifice. The inlet orifice is located downstream of an air mass meter measuring the air mass flowing into the cylinders of the internal combustion engine and upstream of a throttle valve. The secondary air system comprises a secondary air valve which is installed in the secondary air pipe and a control device with a monitoring unit which controls the degree of opening of the secondary air valve. The monitoring unit, which includes a physical model of the intake tract and the secondary air system, determines an estimated value of a secondary air mass flow as a function of the aperture angle of the throttle valve, the revolutions per minute, and a measured value of a first air mass flow determined by the air mass meter.
DE 196 09 922 A1 discloses a method for monitoring the secondary air injection in the case of an internal combustion engine having a measuring sensor for measuring the oxygen content in the exhaust gas. The method is based on the reaction of the measuring sensor to the switching-in of the secondary air, the volume of the air aspirated by the internal combustion engine being increased during the supply of air to the exhaust gas.
DE 102 49 421 A1 discloses a method for monitoring the delivery of secondary air to the exhaust gas of an internal combustion engine, wherein the internal combustion engine has at least two partially separate exhaust gas systems in each which are disposed an exhaust gas catalyzer and, upstream thereof, a lambda probe. A secondary air pump is provided which delivers the drawn-in secondary air initially via a single secondary air line containing an electrically controllable secondary air valve and which branches off downstream of the secondary air valve into a number of individual secondary air lines corresponding to the number of exhaust gas systems for the purpose of delivering secondary air to the respective exhaust gas systems. A value for the total air mass flow that is introduced into the exhaust gas systems is determined from the signal of at least one air mass meter. In order to determine the actual air mass introduced into the individual exhaust gas systems, the output signals from the lambda probes in the exhaust gas systems are referred to in order to identify an uneven distribution of the air mass supplied to the individual exhaust gas systems.
DE 100 65 963 A1 discloses an apparatus for supplying secondary air on an individual cylinder basis to the exhaust gas of an internal combustion engine, said apparatus having at least two partially separated exhaust gas pipes and a secondary air pump having secondary air conduits which connect the outlet side of the secondary air pump to one of the aforesaid separate exhaust gas pipes in each case. A separately controllable flow control means is provided in each of the said secondary air conduits. Additionally provided on the outlet side of the secondary air conduit is at least one further controllable opening whose opening state influences the pressure in the said secondary air conduits. A diagnosis of the individual secondary air conduits is not addressed.